This invention concerns a dosing device and in particular relates to dosing devices for drug delivery such as injectors and inhalers, and a mechanism for use in such devices.
In treatment for asthma and other respiratory problems, a patient may take medication into his lungs by inhaling either an aerosol mist or a cloud of fine particles from an inhaler. Conventional asthma inhalers fall into two categories: xe2x80x98dry powder inhalersxe2x80x99 and xe2x80x98metered dose inhalersxe2x80x99 (MDI""s).
Breath operated MDI""s are known. For example U.S. Pat. No. 3565070 describes an xe2x80x98inhalation actuable aerosol dispenserxe2x80x99 and in addition WO 92/09232 and European patent 0147028 disclose further examples of breath operated MDI""S.
An MDI consists of a small canister containing medication with a metering valve and a valve stem. The MDI delivers a metered dose to the patient when the valve stem is pressed. The fundamental problem in the design of breath operated MDI""s is that a large force (of the order of 30 N) is required to depress the valve stem and actuate an MDI. However only a very small force is available from the patient""s breath. This problem is partly overcome in the prior art by manually compressing a large spring to a sufficient force to actuate the device. The spring is compressed by the patient, either by a positive xe2x80x98cockingxe2x80x99 process or automatically when the patient opens the mouthpiece cover. The spring is then released by a trigger operated by the patient""s breath. The operation of the trigger is however difficult to engineer reliably and cheaply since releasing a spring with a stored force of 30N using a low force from the patient""s breath is a difficult technical challenge.
WO 92/09323 describes a pneumatic system for holding the stored force. This requires a number of components which must be carefully manufactured to maintain a satisfactory vacuum seal during operation. European patent 0147028 describes a mechanical trigger design which requires extremely tight manufacturing tolerances and which to some extent depends on consistent levels of friction for repeatable operation.
The present invention seeks to provide an inhaler with a dose actuation mechanism which provides a very substantial amplification of the force being available from a patient""s breath, whilst not being vulnerable to changes in the coefficient of friction between moving parts.
According to the present invention, there is provided a dosing device comprising a dispensing means for dispensing a dose material, and a dose actuation mechanism, in which the dose actuation mechanism comprises a readily deflectable member, and a series of at least two movable elements which transmit and magnify movement of the first element in the series to the last element in the series by a cascade effect, wherein the deflectable member is movable by airflow, and its movement is transferred to the first element of the said series so as to actuate the dispensing means.
Preferably the moveable elements are pivoted and arranged sequentially to inter-communicate, movement of a first pivoted element by the deflectable member effecting movement of at least another pivoted element so as to actuate the dispensing means.
The deflectable member is preferably movable in response to inhalation by a patient. Thus in use only inhalation by the patient is required to activate the dose actuation mechanism and thus cause the measured dose to be dispensed.
The use of a cascade of moveable pivoted elements provides a form of amplification of the originating force created by the intake of breath, and whilst any number of such elements may be employed in the cascade, in general two such elements are sufficient.
As a preferred feature of the invention, this amplification may be achieved by a first biasing means which communicates with one moveable element so that as movement is transferred between the moveable elements, energy stored in the first biasing means is released to increase the force associated with the movement. This ensures that a small initial force exerted on the deflectable member is increased in magnitude as it cascades through the moveable elements. In such a way, a small initial force is magnified to allow actuation of the dispensing means.
Preferably one moveable element remote from the deflectable member is attached to, or acts on, the dispensing means so as to restrain actuation thereof until the said moveable element is deflected as a result of a cascade action. In this way the movement of the deflectable member and the pivoted elements can be used to release stored energy to provide sufficient force to dispense a dose from the dispensing means. In particular the dispensing means may be associated with a second biasing means, in which energy is stored in compression, which stored energy is released on movement of a pivoted element.
The invention also lies in a dose actuating mechanism for use in a dosing device, comprising a deflectable member and a cascade of at least two moveable elements, movement of the deflectable member being transferred to and between the moveable elements, in such a manner as to trigger the release of stored energy sufficient to release a dose.
Preferably the dosing device is also provided with a lid including at least one cam surface, wherein movement of the lid results in the pivoted elements being restored to positions of unstable equilibrium ready to cause actuation of the dispensing means when the cascade is triggered.
The pivoted elements are preferably movable into a first position of unstable equilibrium, which movement is translated into stored energy, in the second biasing means, and when triggered, move into a second position of equilibrium, during which movement the stored energy is released from the second biasing means to dispense a dose from the dispensing means.
Preferably the moveable pivoted elements each comprise over-centre mechanisms. Thus where the over-centre mechanisms are arranged sequentially, movement of a first over-centre mechanism in the cascade, triggered by movement of the deflectable member, results in subsequent movement of the next, and in turn, any subsequent over-centre mechanisms, the last of which allows for actuation of the dispensing means.
Particularly preferred is the use of a first and a second over-centre mechanism as the moveable elements, the first over-centre mechanism communicating with first biasing means and the second over-centre mechanism communicating, via the dispensing means, with a second biasing means.
The use of two over-centre mechanisms in this way provides a force cascade which eventually results in actuation of the dispensing means. Thus an initial small force produced by movement of air due to inhalation, moves the deflectable member, which movement causes a first over-centre mechanism to shift over-centre, to produce an increased intermediate force because of the action of the first biasing means, this intermediate force in turn causes a second over-centre mechanism to shift over-centre to release a larger stored force, typically 30N, from a second biasing means, so as to operate the inhaler. The use of over-centre mechanisms allows for a very substantial force amplification whilst reducing the effect of changes in the co-efficient of friction between moving parts.
The dose actuation mechanism of the present invention is applicable to various inhalers where breath actuation is desirable and where the drug is delivered by the release of stored energy in a spring. For example there is a family of devices known as pump jets in which the drug is delivered under pressure through a nozzle by the action of a mechanical pump, typically a piston pump. These have been used in the past for nasal drug delivery and for perfumes where the droplet size is not as critical as for inhaled drugs but they are now being developed to the point where very small droplets can be produced, suitable for inhalation. The mechanical pump may be driven by a powerful spring which is released by the patient""s inhalation. The present invention is suitable for this type of inhaler either used in the mouth or for nasal drug delivery.
There are also some types of dry powder inhaler (DPI) in which the release of the drug particles is assisted by air movement caused by a piston driven by the release of a compressed spring or the drug particles are mechanically released by the direct action of a triggered spring. Again there is a need for a trigger mechanism capable of being reliably triggered by a small force, and thus the present invention is also applicable for these inhalers.
The present invention is also applicable in other fields where force amplification is valuable, for example other drug delivery and medical devices where stored energy is released by a manually operated trigger. Examples of this are needle-free injection systems (both with liquid drug and powder) in which the drug is accelerated towards the patient""s skin through the release of stored energy, auto-injectors in which a conventional syringe and needle are actuated by the release of stored energy and nasal or topical sprays in which the dosing pump is spring actuated.